1. Field of the Invention
The present invention relates to a method of liquefying coal by hydrogenation or hydrogenolysis of coal under high temperature and high pressure conditions, and in the presence of a coal liquefaction catalyst, thereby hydrogenating coal that has been placed in a solvent for the specific purpose of liquefaction.
2. Description of the Prior Art
Coal liquefaction methods include the direct liquefaction method wherein hydrogen is added at a high temperature and a high pressure so as to perform hydrogenolysis. In this method, a large amount of hydrogen is consumed, and the hydrogenation reaction conditions are severe. In order to moderate the reaction conditions, various catalysts are conventionally used, e.g., oxides or halides of cobalt, molybdenum, tungsten, tin, iron or lead, and the reaction is allowed to take place in the presence of a catalyst selected from these catalysts. However, none of these catalysts satisfies all the properties desired in such an application, i.e., high liquefaction activity, low cost, and availability in large amounts.
For example, in the conventional H-Coal method, 1 to 10 parts by weight of a Co-Mo based pellet catalyst are charged in a boiling water reaction tower based on 100 parts by weight of coal; coal slurry is passed through the tower, and coal is allowed to react with hydrogen at a temperature of about 450.degree. C. and a hydrogen pressure of 150 to 220 kg/cm.sup.2. However, since this catalyst is expensive, the method is prohibitively expensive.
A known method using iron ore as a ferric catalyst has the advantage of availability in large amounts, since iron ore is inexpensive. However, this advantage aside, if untreated, such a catalyst has a low liquefaction activity. For this reason, sulfur or a compound of sulfur is added as a promotor to improve liquefaction activity. Unfortunately, when sulfur or its compound is used in a large amount, sulfur or the sulfur compound is evident in the liquefied oil, thereby degrading its quality.